The present invention relates to emulsifiable waxes, comprising copolymers of
from 90 to 95% by weight of ethylene,
from 4 to 10% by weight of one or more C3-C12 alkenecarboxylic acids, and
from 0 to 1.2% by weight of one or more tertiary esters of the corresponding C3-C12 alkenecarboxylic acids,
where the wax has a cinematic melt viscosity of from 800 to 3000 mm2/s, measured at 120xc2x0 C.
The invention further relates to a process for preparing the novel emulsifiable ethylene polymers, to emulsions comprising the novel ethylene polymers, to a process for preparing the emulsions from the novel ethylene polymers, and also to floor cleaners, car cleaners, leather cleaners and stone cleaners, and to coatings for surfaces made from wood, metal, paper, glass or from plastics, comprising aqueous emulsions of the novel emulsifiable waxes.
Emulsifiable ethylene polymers are of great interest industrially, since they can be used as low-cost floor cleaners or processing aids, for example. Other applications are hot-melt adhesives, for metals, ceramics, wood, glass, leather or plastics, and also adhesion promoters for coatings made from polyolefins or from rubbers, and additives for paints. The emulsifiable ethylene polymers known industrially are oxygen-containing ethylene polymers in which the oxygen can be introduced in two different ways:
by free-radical or Ziegler-Natta polymerization of ethylene, followed by oxidation of the resultant polyethylene waxes by air or peroxides, or by pure oxygen, or by mixtures of the same, giving what are known as oxidate waxes, or
by free-radical copolymerization of ethylene with acrylic acid or methacrylic acid or with hydrolyzable acrylates or with methacrylates, with malonates, or with vinyl carboxylates, such as vinyl acetate, under high-pressure conditions, again introducing oxygen functionalities into the polyethylene chain.
However, both processes have disadvantages industrially. The oxidation of a polyethylene reduces the molecular weight of the fundamental polyethylene chains, and this is disadvantageous for the hardness of the product. Finally, the production of oxidate waxes is always a two-stage process, requiring additional capital expenditure (cf. Ullmann""s Enyclopxc3xa4die der technischen Chemie, 4th edition, key words: Wachse, Vol. 24, pp. 36 et seq., Thieme Verlag Stuttgart, 1977, for example).
It is in fact possible to copolymerize ethylene directly with acrylic acid. However, the direct use of acrylic acid as comonomer in industrial plants is undesirable, since acrylic acid is corrosive in those sections of the plant disposed to mechanical stress, for example compressors, feed pipes and valves.
If an ester hydrolysis step has to be inserted after the polymerization in preparing a polyethylene wax, the result is a two-stage process with the associated disadvantages of high capital expenditure requirement.
DE-A 25 24 274 describes a process for preparing polymers made from ethylene and tert-butyl acrylate or tert-butyl methacrylate, polymerizing in a reactor and giving the resultant ethylene-tert-butyl acrylate-acrylic acid terpolymer a thermal post-treatment in a second reaction zone. The thermal post-treatment cleaves a certain percentage of the ester groups. The polymers known from the literature have very good film properties and provide good film material. However, the terpolymers prepared are unsuitable as waxes.
It is also known that tert-alkyl esters of acrylic acid or methacrylic acid can be copolymerized with ethylene by a free-radical route. These esters can be hydrolyzed under acid or alkaline conditions, and can also be cleaved thermally.
U.S. Pat. No. 3,132,120 describes the preparation of ethylene-tert-butyl methacrylate copolymers followed by thermolysis at from 275 to 350xc2x0 C. in the absence of a substantial amount of oxygen. This is a two-stage process which requires high capital expenditure.
DE-A 43 34 846 describes a process for preparing carboxyl-containing copolymers of ethylene, featuring subsequent thermolytic cleavage of the ester groups of tertiary alcohols at from 150 to 250xc2x0 C. in the presence of sulfonic acids. The process is characterized by the substantial absence of initiators for free-radical reactions. This, too, is a two-stage process.
DE-A 42 19 129 describes a procedure for the copolymerization of ethylene with n-butyl acrylate or tert-butyl acrylate in a tubular reactor which is operated at different temperatures in the different reaction zones. This procedure can give copolymers with good film properties, but not emulsifiable waxes.
DE-A 29 37 239 describes a process for preparing copolymers of ethylene by copolymerizing ethylene with esters of unsaturated carboxylic acids, and, in a second step reacting these at from 40 to 75xc2x0 C. with compounds conventionally used for ester hydrolysis, in particular with concentrated H2SO4. This second step consumes time and needs high capital expenditure. In addition, contaminated solvents are produced, and are expensive to purify or dispose of.
Finally, DE-A 17 70 777 describes a process for preparing waxy copolymers of ethylene, in which ethylene, C3-C12 alkenecarboxylic acids, tert-alkyl esters of the relevant C3-C12 alkenecarboxylic acids, and also isobutene, are copolymerized by a free-radical route at from 110 to 350xc2x0 C. and at pressures of from 100 to 4000 atm. A preferred embodiment mentioned is polymerization in a tubular reactor, and the temperature profiles are described in detail. However, the waxy copolymers obtainable by way of this teaching no longer meet the requirements of today""s markets. For example, depending on the embodiment they comprise excessive proportions, i.e. more than 1% by weight, of uncleaved ester groups, making the waxes tacky. In another embodiment of DE-A 17 70 777, the proportions of acrylic acid copolymerized are too low, giving unsatisfactory emulsifiability. Finally, there are embodiments in which the viscosity, for example that determined by way of the cinematic viscosity, is too low, so that performance characteristics deteriorate. For example, floor cleaners produced using low-viscosity waxes lack adequate hardness. Lastly, performance testing shows that the copolymers obtainable by the process disclosed in DE-A 17 70 777 are chemically inhomogeneous. This inhomogeneity, caused for example by the differences in comonomer contents of the different polymer molecules, becomes noticeable in a relatively high speck count.
The wax obtainable as in DE-A 17 70 777 can be post-treated by prolonged heating, but this risks degradation of the polymer chains, or else crosslinking of the polymer. Crosslinked polymers in turn give a high speck count in performance tests. It would also be possible to ensure chemical homogeneity by, for example, feeding tert-butyl acrylate into the tubular reactor at a very large number of locations. However, the high pressures make this procedure disadvantageous for technical and cost reasons. Either numerous very high-performance pumps are required or severe pressure loss would have to be accepted.
It is an object of the present invention, therefore,
to provide emulsifiable waxes comprising ethylene-tert-butyl acrylate-acrylic acid copolymers which have a very low speck count, have adequate viscosity, are not tacky and can be prepared under cost-effective conditions,
to provide a process for preparing the desired waxes,
to prepare aqueous emulsions from the desired waxes, and
from the emulsions of the emulsifiable waxes to prepare floor cleaners, car cleaners, leather cleaners and stone cleaners, and also coatings for surfaces made from wood, metal, paper, glass or from plastics.
We have found that this object is achieved and that the novel emulsifiable waxes can be obtained by copolymerizing ethylene and one or more tertiary esters of one or more C3-C12 alkenecarboxylic acids, preferably tert-butyl acrylate, in a stirred high-pressure autoclave at an elevated temperature, thermally cleaving the ester group during this same step, and carrying out these operations at a substantially constant temperature. The temperature during the reaction here is identical across the entire reactor. No significant chronological or spatial temperature differences occur, and these are on average less than 5xc2x0 C., preferably less than 3xc2x0 C. The setting of a temperature profile, as in DE-A 42 19 129, is therefore dispensed with.
It is also important that from the very beginning of operations an elevated temperature is used. For the purposes of the present invention, an elevated temperature is from 240 to 340xc2x0 C., preferably from 260 to 300xc2x0 C. Higher temperatures can cause partial decomposition of monomers, or else crosslinking of the product, and this causes speck formation in performance testing. At lower temperatures there is insufficient cleavage of the tert-butyl groups.
The pressure conditions are less critical. Suitable pressures are from 1000 to 3500 bar, preferably from 1500 to 2500 bar. These pressures are standard conditions for high-pressure polymerization processes.
The stirred high-pressure autoclaves preferably employed for this process are known per se, and a description is found in Ullmann""s Enyclopxc3xa4die der technischen Chemie, 4th edition, keywords: Wachse, Vol. 24, pp. 36 et seq;, Thieme Verlag Stuttgart, 1977). Their length/diameter ratio is mainly from 5:1 to 30:1, preferably from 10:1 to 20:1.
The monomers used comprise ethylene, and also one or more tertiary esters of one or more C3-C12 alkenecarboxylic acids. If desired, other monomers copolymerizable under the reaction conditions may be added. 1-Olefins, such as propene or 1-butene, may be used here, as may isobutene.
Examples of suitable C3-C12 alkenecarboxylic acids are: acrylic acid, methacrylic acid, vinylacetic acid, crotonic acid, maleic acid and fumaric acid, preferably acrylic acid or methacrylic acid, particularly preferably acrylic acid.
Examples of suitable tertiary ester groups are: tert-butyl, tert-amyl or neophyl, and tert-butyl is particularly preferred.
The makeup of the comonomer feed may be varied within certain limits. It is generally from 1.5 to 8% by weight of a tertiary ester of a C3-C12 alkenecarboxylic acid or else of the mixture of corresponding esters. From 2 to 7% by weight are preferred, and from 2.5 to 6.7% by weight are particularly preferred. The balance of 100% by weight is given as ethylene.
The polymers may also contain small amounts of isobutene, of the order of 2% by weight. The isobutene is formed by thermolytic cleavage of tertiary butyl groups. However, determination by analysis is difficult, since the appropriate signals overlap strongly, both in the NMR measurements frequently used and in IR measurements. The copolymerized isobutene units are therefore usually ignored in analysis.
The values for the makeup of the comonomer feed are particularly useful if the overall conversion is set at from about 30 to 35%. If a lower conversion is to be realized, the percentages of tertiary ester which have to be fed are generally smaller.
The initiators used for the free-radical polymerization may comprise the usual free-radical initiators, such as organic peroxides, oxygen or azo compounds. Combinations of the abovementioned free-radical initiators are also suitable. Particularly suitable peroxides are di-tert-butyl peroxide, tert-butyl peroxypivalate, tert-butyl peroxyisononanoate and dibenzoyl peroxide, or mixtures of the same. An example of an azo compound is azobisisobutyronitrile (AIBN). The amounts of the free-radical initiators fed are those usual for polymerization.
Regulators usual for high-pressure polymerization may be added to the reaction mixture, for example alkanes, such as propane or isododecane, alkenes, such as propylene, aldehydes, such as propionaldehyde or benzaldehyde, or ketones, such as acetone or methyl isobutyl ketone.
The novel waxes can be obtained by the process described above. These novel waxes have the following features:
The melting points of the novel waxes are from 60 to 110xc2x0 C., preferably from 80 to 105xc2x0 C. Waxes with lower melting points are disadvantageous when used in floor cleaners or car cleaners, since they lack adequate mechanical stability when the temperature rises, for example in the summer. Waxes with higher melting points give markedly poorer emulsification.
The acid number determined DIN 53402, is from 30 to 110 mg KOH/g of wax, preferably from 30 to 65 mg KOH/g of wax and particularly preferably from 30 to 50 mg KOH/g of wax.
The proportion of unthermolyzed tertiary ester groups should be very low. The preferred lower limit is 0.3% by weight and particularly preferably 0.02% by weight. Cleavage of all of the ester groups requires a prolonged reaction time and is therefore rather unattractive economically. In addition, a prolonged reaction time can lead to increased thermal stress on the wax to be prepared and to degradation of the polymer chains or to crosslinking reactions.
The maximum proportion of unthermalized ester groups is 1.2% by weight, preferably 1% by weight and particularly preferably 0.5% by weight. Higher proportions make samples of wax tacky. The preferred method for determining the proportion of ester groups is NMR spectroscopy.
The proportion of acid units in the novel wax, particularly preferably of acrylic acid units, is at least 1.2% by weight, preferably at least 2% by weight and particularly preferably at least 4% by weight. Smaller proportions of acid units lead to poorer emulsifiability of the waxes. The slip resistance moreover of floor cleaners prepared using a novel wax is good only at more than 1.2% by weight of acid units.
On the other hand, the proportion of acid groups should not exceed 10% by weight, preferably 8.5% by weight, and particularly preferably 8% by weight, because the ester component from which the acid groups have been produced is markedly more expensive than ethylene.
The cinematic melt viscosity, measured at 120xc2x0 C., of the novel waxes is from 800 to 3000 mm2/s, preferably from 1000 to 2000 mm2/s. Lower melt viscosities lead to unsatisfactory mechanical properties of the floors after cleaning. If the melt viscosities are too high it becomes impossible to emulsify the waxes satisfactorily.
The novel waxes may be emulsified by processes known per se. For this, the wax is melted in an autoclave and the following mixture, for example, is prepared:
from 10 to 80 parts by weight of the polymer of the invention,
from 2 to 10 parts by weight of an emulsifier, ionic and nonionic surfactants being suitable and nonionic surfactants being preferred. Examples of commonly used nonionic emulsifiers are ethoxylated mono-, di- and trialkylphenols (EO number: from 3 to 50, alkyl: C4-C12) and also ethoxylated fatty alcohols (EO number: from 3 to 80, alkyl: C8-C36). Preferred examples of these are the Lutensol(copyright) grades from BASF AG, but other products, such as Triton(copyright) grades from Union Carbide, are also suitable,
from 0.1 to 5 parts by weight, preferably from 0.5 to 1 part by weight, of an alkali metal hydroxide, preferably NaOH or KOH;
from 0.01 to 1 part by weight of an acid scavenger, sodium disulfite being particularly suitable, and
from 20 to 200 parts by weight of water, preferably from 60 to 70 parts by weight.
Temperature and pressure conditions for preparing the novel emulsions are not critical per se. A wide range of temperatures may be used, preferably above the melting point of the novel wax to be emulsified. The pressure range from 1 to 10 bar is suitable. The mixing time after complete melting of the wax is usually from 2 minutes to one hour. Operations are generally carried out with stirring under inert conditions, i.e. under nitrogen.
The emulsions prepared according to the invention may be used in the following applications, which are given as examples: hot-melt adhesives, processing of thermoplastics (e.g. polyamide, impact-modified polystyrene, ABS or polypropylene), (water-based) surface coatings, two-layer metallic automotive paints, masterbatches (pigment concentrates for coloring polyolefins, for example), coating of metal surfaces, wood surfaces, paper, glass, or of plastics, or adhesives, impregnation of construction materials, floor protection, cleaners (e.g. leather or stone cleaning), car cleaners, floor cleaners, bottle coatings or mold release agents.
It is particularly preferable to use the novel emulsions in floor cleaners, in car cleaners, in leather cleaners and in stone cleaners, or else in coatings for surfaces made from wood, metal, paper, glass or from plastics.
The capacity of the novel emulsions to form colorless, clear glossy films can be utilized in floor cleaners. They can moreover improve the slip resistance and the usage qualities of floors.
A typical test floor cleaner is composed of
from 10 to 20 parts by weight of the novel emulsions, which are responsible for elasticity, dirt-repellency and gloss of the floor to be cleaned,
from 0.5 to 5 parts by weight, preferably from 2 to 3 parts by weight, of ethylene diglycol,
from 0.1 to 10 parts by weight, preferably from 1 to 2 parts by weight, of ethylene glycol,
from 0.1 to 10 parts by weight, preferably from 1 to 2 parts by weight, of a permanent plasticizer, trialkyl phosphates being examples of plasticizers used, particularly preferably tri(n-butoxyethyl) phosphate,
from 0.1 to 5 parts by weight, preferably from 0.5 to 1.5 parts by weight, of a wetting and leveling agent, the wetting and leveling agents usually used being fluorinated surfactants, such as FC-129 from 3M, and,
from 20 to 30 parts by weight of a dispersion made from polystyrene-acrylate as carrier. A preferred example is Poligen(copyright) MF750.
The test floor cleaner is prepared by mixing the components in a bucket, and it is generally sufficient if these are stirred together for 5 minutes.